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Simple Comparison (simple + comparison)
Selected AbstractsAre forest birds categorised as "edge species" strictly associated with edges?ECOGRAPHY, Issue 4 2003Louis Imbeau In recent years, studies of bird-habitat relationships undertaken in the context of habitat fragmentation have led to the widespread use of species categorisation according to their response to edge alongside mature forest patches (edge species, interior species, interior-edge generalist species). In other research contexts, especially in less fragmented landscapes dominated by a forested land base in various age classes, bird-habitat relationships are often described in relation to their use of various successional stages (early-successional species, mature forest species, generalist species). A simple comparison of these two commonly-used classifications schemes in a close geographical range for 60 species in eastern North America as well as for 36 species in north-western Europe clearly reveals that in these two particular biomes the two classifications are not independent. We believe that this association is not only a semantic issue and has important ecological consequences. For example, almost all edge species are associated with early-successional habitats when a wide range of forest age-classes are found in a given area. Accordingly, we suggest that most species considered to prefer edge habitats in agricultural landscapes are in fact only early-successional species that could not find shrubland conditions apart from the exposed edges of mature forest fragments. To be considered a true edge species, a given species should require the simultaneous availability of more than one habitat type and consequently should be classified as a habitat generalist in its use of successional stages. However, 28 out of 30 recognised edge species were considered habitat specialists in terms of successional status. Based on these results, we conclude that "real edge species" are probably quite rare and that we should make a difference between true edge species and species which in some landscapes, happen to find their habitat requirements on edges. [source] Using propensity scores to estimate the effects of insecticides on stream invertebrates from observational data,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2009Lester L. Yuan Abstract Analyses of observational data can provide insights into relationships between environmental conditions and biological responses across a broader range of natural conditions than experimental studies, potentially complementing insights gained from experiments. However, observational data must be analyzed carefully to minimize the likelihood that confounding variables bias observed relationships. Propensity scores provide a robust approach for controlling for the effects of measured confounding variables when analyzing observational data. Here, we use propensity scores to estimate changes in mean invertebrate taxon richness in streams that have experienced insecticide concentrations that exceed aquatic life use benchmark concentrations. A simple comparison of richness in sites exposed to elevated insecticides with those that were not exposed suggests that exposed sites had on average 6.8 fewer taxa compared to unexposed sites. The presence of potential confounding variables makes it difficult to assert a causal relationship from this simple comparison. After controlling for confounding factors using propensity scores, the difference in richness between exposed and unexposed sites was reduced to 4.1 taxa, a difference that was still statistically significant. Because the propensity score analysis controlled for the effects of a wide variety of possible confounding variables, we infer that the change in richness observed in the propensity score analysis was likely caused by insecticide exposure. [source] Making Efficient Use of Patients in Designing Phase III Trials Investigating Simultaneously a Set of Targeted Therapies with Different TargetsBIOMETRICAL JOURNAL, Issue 6 2006Werner Vach Abstract Targeted therapies are a recent development in cancer treatment research. As these therapies can only be administered to patients with certain individual characteristics, it is a straightforward idea to investigate several of such therapies simultaneously in a given patient population in order to compare each targeted therapy with the current standard therapy. This raises the question how patients satisfying several characteristics should be handled. We consider in this paper several designs to allocate treatments in a random manner to these patients, such that the evaluation of each single targeted therapy can be based on a simple comparison of patients receiving the targeted therapies versus those receiving the standard therapy within a well defined subgroup of patients satisfying the corresponding characteristic. We show how one can ensure that patients with several characteristics can contribute simultaneously to the evaluation of several targeted therapies and that this is the key point for an efficient use of the patients available. We further discuss some ethical and practical issues in applying the new designs and outline strategies to evaluate the overall effect of all targeted therapies together. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Determining Molecular Structures and Conformations Directly from Electron Diffraction using a Genetic AlgorithmCHEMPHYSCHEM, Issue 2 2006Scott Habershon Dr. Abstract A global optimization strategy, based upon application of a genetic algorithm (GA), is demonstrated as an approach for determining the structures of molecules possessing significant conformational flexibility directly from gas-phase electron diffraction data. In contrast to the common approach to molecular structure determination, based on trial-and-error assessment of structures available from quantum chemical calculations, the GA approach described here does not require expensive quantum mechanical calculations or manual searching of the potential energy surface of the sample molecule, relying instead upon simple comparison between the experimental and calculated diffraction pattern derived from a proposed trial molecular structure. Structures as complex as all- trans retinal and p -coumaric acid, both important chromophores in photosensing processes, may be determined by this approach. In the examples presented here, we find that the GA approach can determine the correct conformation of a flexible molecule described by 11 independent torsion angles. We also demonstrate applications to samples comprising a mixture of two distinct molecular conformations. With these results we conclude that applications of this approach are very promising in elucidating the structures of large molecules directly from electron diffraction data. [source] The Air is Always Cleaner on the Other Side: Race, Space, and Ambient Air Toxics Exposures in CaliforniaJOURNAL OF URBAN AFFAIRS, Issue 2 2005Manuel Pastor Jr. This article uses U.S. EPA's National Air Toxics Assessment (NATA) for 1996 to examine environmental inequality in California, a state that has been a recent innovator in environmental justice policy. We first estimate potential lifetime cancer risks from mobile and stationary sources. We then consider the distribution of these risks using both simple comparisons and a multivariate model in which we control for income, land use, and other explanatory factors, as well as spatial correlation. We find large racial disparities in California's "riskscape" as well as inequalities by other factors and suggest several implications for environmental and land use policy. [source] Implications of family environment and language development: comparing typically developing children to those with spina bifidaCHILD: CARE, HEALTH AND DEVELOPMENT, Issue 5 2009B. Vachha Abstract Introduction This study examines the effect of family environment on language performance in children with myelomeningocele compared with age- and education-matched controls selected from the same geographic region. Methods Seventy-five monolingual (English) speaking children with myelomeningocele [males: 30; ages: 7,16 years; mean age: 10 years 1 month, standard deviation (SD) 2 years 7 months] and 35 typically developing children (males: 16; ages 7,16 years; mean age: 10 years 9 months, SD 2 years 6 months) participated in the study. The Comprehensive Assessment of Spoken Language (CASL) and the Wechsler tests of intelligence were administered individually to all participants. The CASL measures four subsystems: lexical, syntactic, supralinguistic and pragmatic. Parents completed the Family Environment Scale (FES) questionnaire and provided background demographic information. Standard independent sample t -tests, chi-squared and Fisher's exact tests were used to make simple comparisons between groups for age, socio-economic status, gender and ethnicity. Spearman correlation coefficients were used to detect associations between language and FES data. Group differences for the language and FES scores were analysed with a multivariate analysis of variance at a P -value of 0.05. Results For the myelomeningocele group, both Spearman correlation and partial correlation analyses revealed statistically significant positive relationships for the FES ,intellectual,cultural orientation' (ICO) variable and language performance in all subsystems (P < 0.01). For controls, positive associations were seen between: (1) ICO and lexical/semantic and syntactic subsystems; and (2) FES ,independence' and lexical/semantic and supralinguistic tasks. Conclusions The relationship between language performance and family environment appears statistically and intuitively sound. As in our previous study, the positive link between family focus on intellectually and culturally enhancing activities and language performance among children with myelomeningocele and shunted hydrocephalus remains robust. Knowledge of this relationship should assist parents and professionals in supporting language development through activities within the natural learning environment. [source] | |||||||||||||